Earphones have become very popular as more and more people wear portable electronic devices, such as mp3-players and mobile phones.
There are a variety of sizes of the earphones, of which a few a large and encompass the entire outer ear when worn by a user, whereas others are small and are designed to be inserted into the ear canal of the user.
From EP 0517497 it is known an earphone designed like an earplug to be inserted into the ear canal. This earplug is further adapted to shut the auditory meatus of an ear in use, so as to acoustically isolate the external auditory meatus from the outside of the ear.
From U.S. Pat. No. 5,887,070 a high fidelity insert earphone and methods of making same are known. This earphone is provided with a damper and receiver are mounted such that the damper and receiver response compensates for loss of external ear resonance and coupling resonance that otherwise would occur when the insert earphone is inserted into the ear canal.
US 2006/0165249 A1 teaches a small earphone or headphone that can produce a wide band acoustic output from a low-pitched tone to a high-pitched tone and can generate a body-sensitive vibration independent output or a body-sensitive vibration output synchronized with music.
Electro active polymers (EAP) are characterised by their ability to change shape in response to electrical stimulation. The electro-active polymers may be categorised in two major groups, one being electrostatic EAPs, and the other being ionic EAPs. The electro static EAPs as today typically require a voltage of the order of kilo Volts to generate a substantial shape change, the ionic EAPs currently available show shape changes as a response to voltages of the order of Volts.
An electro-active polymer (EAP) device 100, 120 according to the prior is illustrated in FIGS. 1A and 1B. In FIG. 1A the EAP device 100 comprises an upper electrode 102, a lower electrode 104 and an EAP portion 106. The upper and lower electrodes 102, 104 are arranged opposite in relation to one another, surrounding the EAP portion 106.
In FIG. 1B an electro-active polymer device 120 is shown onto which an electric voltage 128 has been applied between an upper electrode 122 and a lower electrode 124, wherein the lower electrode is connected to ground potential. The two electrodes 122 and 124 surround the EAP portion 126, providing an electric field across the EAP causes a shape change of the EAP. The EAP device 120 typically shrinks in the direction of the electric field lines between the two electrodes 122 and 124, whereas the EAP device 120 typically expands in a direction perpendicular to these field lines. The EAP device 120 may thus expand in a direction parallel with the electrodes 122 and 124, as a consequence of the applied electric potential V, 128.
Albeit the large number of earphones disclosed, there is still a need for improving the sound provision to the wearers of the earphones.